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Twinn Stack air compressor

04-29-2012, 12:10 PM

was working on a project and compressor tried starting after pressure went down and tripped the breaker reset the breaker and tried again..tripped a second time..bled the pressure off all the way and it started up again.I have the twinn stack model number 45-150A any answers to my problem thank you

Comment

I'm happy to hear that in this particular case you found it to be a weak circuit breaker. Usually these symptoms are a failed "pressure relief" (unloader) valve, which is usually located on the pressure switch.

To explain: As the compressor starts up, it should (and cannot) have no pressure in the cylinder. As pressure is built, it's piped from the cylinder outlet through a "check valve" into the tank. The "check valve" is a one-way valve...allowing the air to build within the tank, but not flow back out of the tank to the cylinder. Depending on how the system was designed, at some point in this line between the cylinder outlet and the tank check valve, there is an "unloader" line that goes back to the often-troublesome unloader "relief valve" that is triggered by the pressure switch. (This "relief valve" is totally different than the "safety valve")

So, what happens is that the cylinder builds the pressure, it flows to the tank where it builds to the tanks working pressure. The tank is monitored by the pressure switch (separately connected to the tank) and as soon as it senses the maximum pressure in the tank, it cuts off the electricity to the motor and at the same time, triggers this "relief valve" which then blows the pressure in that "unloader" line which runs back to the feed line to the tank. This "unloading" blows not only the air from the line, but also from the cylinder. The "check valve" where that line feeds the tank, prevents any pressure from coming back out of the tank. Thus, only that "unloader line" and the cylinder is relieved of pressure.

If you listen at the moment when the compressor shuts off, you can usually hear that quick shot of air, escaping when that relief valve unloads.

But, if the "relief valve" malfunctions when the pressure switch shuts off the motor, that pressurized air is left in the unloader line AND in the cylinder. When the pressure in the tank drops to the point where the pressure switch once again switches on electricity to the motor... that unrelieved pressure in the cylinder cannot be overcome by the motor and it will then most likely be overloaded and trigger the circuit breaker.

If you drained the tank of pressure, the pressure in the "unloader line" would then drain off through the check valve and into the tank; the cylinder and line would be as empty as the tank and you could once again start the compressor and it would go through the cycle again... but with the same results, since the "relief valve" failure to "unload".

This appears to be a often reported problem, and I thought I should attempt to clarify what is happening. While it was a "weak breaker" in this instance and often can be a too resistive extension cord, it too can be this "relief valve" failure to properly "unload".